Micro organisms friend and foe class 8th

 

NOTES PREPARED BY 
ASHAQ HUSSAIN BHAT 
TEACHER SCHOOL 
EDUCATION DEPARTMENT 
JAMMU AND KASHMIR

"Microorganisms: Friends And Foe"

KEYWORDS

•Microbes: Living organisms around us which we cannot see with unaided eye.

•Viruses: They reproduce only inside the host organisms and these are dangerous.

•Protozoa: It is a unicellular micro-organism and causes diseases like dysentery and malaria.

•Fungi: It is a multicellular micro-organism.

•Antibiotics : Medicines to kill or stop the growth of the disease causing micro-organisms.

•Fermentation: The process of conversion of sugar into alcohol.

•Pathogens: Disease-causing micro-organisms.

•Antibodies: Produced by body to fight the invader.

•Nitrogen Fixation: Fixation of nitrogen from air into soil by micro- organisms.

•Anthrax: A dangerous human and cattle disease caused by bacanti-bodies

Text Book Exercise

1. Fill in the blanks:

(a) Microorganisms can be seen with the help of a............... 

(b) Blue green algae fix......... directly from air to enhance fertility of soil.

(c) Alcohol is produced with the help of......... 

(d) Cholera is caused by............. 

Answer: 

Microscope, Nitrogen, Yeast, Bacteria

2. Tick the correct answer:

(a) Yeast is used in the production of

(i) alcohol  ✔                             (ii) sugar

(iii) hydrochloric acid          (iv) oxygen

(b) The following is an antibiotic

(i)Sodium bicarbonate      (ii) Streptomycin✔

(iii) Alcohol                           (iv) Yeast

(C) Carrier of malaria-causing protozoan is

(i) female Anopheles mosquito ✔   (ii)cockroach

(iii) housefly                                    (iv) butterfly

(d) The most common carrier of communicable diseases is

(i) ant                                    (ii) housefly✔ 

(iii) dragonfly                       (iv) spider

(e) The bread or idli dough rises because of

(i) heat                                   (ii) grinding

(iii) growth of yeast cells ✔    (iv) kneading

(1) The process of conversion of sugar into alcohol is called

(i) nitrogen fixation               (ii) moulding

(iii) fermentation   ✔             (iv) infection

3. Match the organisms in Column/with their action in Column Il.

    Column I                        Column II

(i) Bacteria(a)               (a) Fixing Nitrogen

(ii) Rhizobium             (b) Setting of curd

(iii)Lactobacilus         (c) Baking of bread

(iv) Yeast                      (d) Cousing of Malaria

(v)A Protozoa              (e) Causing Cholera

(vi) A virus                   (f) Causing AIDS

                                      (9) Producing antibodies

Answer

I     ➡  e

II    ➡  a

III   ➡  b

IV   ➡  c

V     ➡  d

VI    ➡  f

4. Can microorganisms be seen with the naked  eye? If not, how can they be seen?

Ans:- No, microorganisms can not bee seen with the help of naked eye, they can only be seen with the help of Microscope or in high power magnifying glass because they are very minute in size

5. What are the major groups of microorganisms?

Ans:-The major group of micro organisms are Bacteria , Funji,Protozoa , Algae and virus. 

6. Name the microorganisms which can fix atmospheric nitrogen in the soil.? 

Ans:-Rhyzobium, Cyano bacteria and clostridium are some microorganisms which can fix atmospheric nitrogen in the soil

7. Write 10 lines on the usefulness of microorganisms in our lives.

Ans:- The usefulness of micro organisms are as under ;

i. They are used in converting milk in to curd

ii. They are used in cheese preparation

iii. They are used in the manufacturing of antibiotics

iv. They are used in preparation of alcohol

v. They are considered as cleaning agents because they efficient decomposers

vi. Some of the microorganisms are taken as probiotics

vii. They are used in the production of acetic acid from alcohol

viii. They are used to increase the fertility of soil

ix. They are used as substitutes of proteins. 

x. They are used in bakery industries. 

8. Write a short paragraph on the harms caused by microorganisms.

Ans :- Some   Microorganisms are dangerous to us in so many  ways. For example, microorganisms, known as pathogens cause disease in humans, plants and animals. Pathogens or germs enter a healthy body through air, water, infected food and infected individual by direct or indirect contact or by the carrier. 

Common illnesses like cold, influenza (flu), cough, polio, chicken pox are caused by viruses. Foot and mouth diseases in the livestock are also due to viruses. Typhoid, tuberculosis (TB) are because of bacteria. Anthrax a risky human and livestock sicknesses is also caused by bacteria.

Diseases like dysentery and malaria are caused by protozoa. Ringworm is caused by fungi. Several microbes causes diseases in plants and therefore reduces the yield. Citrus canker, a bacterial disease, affects trees of citrus fruit and is spread by air. Bhendi yellow vein mosaic disease is because of a virus and is spread by insects in lady fingers. Rust of wheat is a fungal disease spread through air. Microorganisms that develop on our food occasionally produce poisonous substances. These make the food toxic causing severe infection and even death. This food-borne illness is referred to as food poisoning.

9. What are antibiotics? What precautions must be taken while taking antibiotics?

Ans:- Antibiotics are the chemicals which kill or stop the growth of disease cousing micro -organisms , they are used to cure various diseases 

While using antibiotics we should take advice of doctor and we must not take antibiotics  un- necessarily. 

ADDITIONAL SHORT ANSWER TYPE QUESTIONS

Q.1. Why certain living organisms are called micro-organisms or microbes?

Ans. The micro-organisms are so small in size that they cannot be seen with the unaided eye and some of these can be seen only by microscope. That is why these are called micro-organisms.

Q.2. Why to add a little curd to warm milk to set curd for the next day?

Ans. Curd contains several micro-organisms, mainly, the bacterium, Lactobacillus, which promote the formation of curd. They start growing in milk and convert milk into curd.

Q.3. Why children / infants are given vaccination?

Ans. By vaccination, a disease carrying microbes enters our body; the body produces antibodies to fight the invader. The body also remembers how to fight the microbe, if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes. This is how a vaccine works.

Q.4. How do you prevent the spread of communicable diseases ?

Ans. We should keep a handkerchief on the nose while sneezing. It is better to keep distance from infected persons.

Q.5. Why teacher keeps telling the students not to let water stagnate anywhere in the neighbourhood?

Ans.All mosquitoes breed in water. Hence, by keeping the surroundings clean and dry we can prevent mosquitoes from breeding. One should not let water collect anywhere viz. in coolers, tyres flower- pots etc.

Q.6. How food can become poisonous ?

Ans. Food poisoning could be due to the consumption of food spoilt by some micro-organisms. Micro-organisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

Q.7. What is pasteurization?

Ans. The milk is heated to 70°C for 15 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

Q.8. Where do micro-organisms live? Write a note.

Ans. Micro-organisms may be single-celled like bacteria and protozoa, or multicellular, such as; algae and fungi, These can survive under all types of environment ranging from ice cold climate to hot springs, desert and marshy lands. They are also found inside the body of animals including humans. Some micro-organisms grow on other organisms, while others exist freely. Micro-organisms like amoeba can live alone, while fungi and bacteria live in colonies.

Q.9. What are communicable diseases ?

Ans. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken-pox and tuberculosis.

Q.10.List few diseases which can be cured and not-cured by antibiotics.

Ans. Several diseases including cholera, tuberculosis, small-pox and hepatitis are prevented by vaccination or antibiotics. Antibiotics, however, are not effective against cold and flu as they are caused by viruses.

Q.11. List few commercial uses of micro-organisms.

Ans. Micro-organisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). For example; Acetobacter aceti bacteria is used for production of acetic acid from alcohol. Yeast is used for commercial production of alcohol and wine by growing 

them on natural sugars present in grains, like; barley, wheat, rice and crushed fruit juices, etc.

Q.12.How antibiotics are manufactured ?

Ans. The antibiotics are manufactured by growing specific micro- organisms and are used to cure a variety of diseases.

Q.13.List few diseases caused by various micro-organisms ?

Ans. Common ailments, like; cold, influenza (flu) and most coughs are caused by viruses. Serious diseases, like; polio and chicken pox are also caused by viruses.

Diseases, like; dysentery and malaria are caused by protozoans.

Typhoid and tuberculosis (TB) are due to bacteria.

Q.14. Write a note on chemical method of food preservation.

Ans. Salts and edible oils are the common chemicals, generally, used to check the growth of micro-organisms. Therefore, they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.

Q.15. How do microbes survive adverse conditions ?

Ans. Micro-organisms are very hardy. They can survive under extreme conditions of temperature and dryness by forming hard outer coating called a cyst. Within this protective shell, they remain inactive as such, until more favourable conditions return. They then emerge from their shell, multiply and go through their life-cycles.

Q.16. Write three ways of entering micro-organisms into the body.

Ans. Entry of micro-organisms into the body :

(i) Through the air we inhale.

(ii) Through the water we drink, and the food we eat.

(iii) Through skin.

Q.17. How do viruses reproduce ?

Ans. Viruses have their own genetic material, but they do not have a cellular structure, nor metabolic activity of their own. Viruses use the energy of the host cell and change their machinery in such a way that they start producing more viral genes. As they multiply and grow in number, the host cell, eventually, bursts releasing all the viral cells.

Q.18. What are nitrogen fixing bacteria? Name one.

Ans. Some micro-organisms have the ability to fix nitrogen present in air (atmosphere). These micro-organisms are the only organism of all plants, animals and micro-organism are able to fix N₂ of air.These micro-organisms are called nitrogen fixing bacteria. For example; Rhizobium.

Q.22. Explain the uses of Bacteria, Fungi and Algae.

Ans. 1. Uses of Bacteria:

(i)It is used to produce vinegar, coffee and tabacco.

(ii) Some bacteria are used to produce antibiotics.

(iii) Lactobacillus converts milk into curd. It also helps in digestion of food.

(iv) Some bacteria help in many functions of our body.

2. Uses of Fungi :

(i) Yeast is used to prepare alcohol and vinegar by fermentation.

(ii) Yeast is used to produce bread, cheese, wine etc.

(iii) Mushrooms are eaten as food.

(iv) Yeast is used to produce vitamin-B.

(v) Penicillin is an antibiotics formed by a fungus called Pencillium.

3. Uses of Algae:

(1) Algae is used to make jellies.

(ii) It is used in soups, ice-creams. Jellies and jams as, thickening agent.

(iii) Chlorella is used to obtain proteins.

(iv) Silica from diatoms is used in toothpastes.

Q.23. What are food preservatives? Explain some common food preservatives.

Ans. The chemical substances, which are used to check or stop the growth of harmful micro-organisms in food are called food preservatives. These food preservatives keep the edible food materials protected from the invasion of micro-organisms, which can spoil the food.

Some common food preservatives are :

(i) Salt: Common salt is used to preserve meat, fish, amla, raw mangoes and tamarind etc.

(ii) Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture contents, which inhibits the growth of bacteria, which spoil food.

Q.24. Write an essay on nitrogen cycle

Ans. Nitrogen Cycle: Our atmosphere consists of 78% nitrogen gas. Nitrogen is one of the essential constituents of all living-organisms, as a part of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen cannot be taken, directly, by plants and animals. The nitrogen fixing bacteria and algae present in the soil fix nitrogen from the atmosphere and convert into nitrite and nitrate forms. Once nitrogen is converted into those usable forms, it can be utilised by plants through their root system. This is the process of 'fixing' of nitrogen. Nitrogen is then used for the synthesis of amino acids, proteins and nitrogenous biomolecules in the plants. Animals feeding on plants get proteins and other nitrogen compounds. When plants and animals die, bacteria and fungi present in the soil convert the various compounds of nitrogen back to nitrates and nitrites. Certain specialized bacteria convert nitrates and nitrites into nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.

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